A recently conducted Phase 0 human clinical trial of riluzole (Rilutek™) demonstrated dramatic efficacy in certain melanoma patients after only 14 days of treatment. Riluzole, the only FDA approved drug to treat amyotrophic lateral sclerosis (ALS), showed clinical or radiologic evidence of tumor response in four of 12 patients with Stage III and IV melanoma, cancer with a poor prognosis and severely limited treatment options.
The use of riluzole (RILUTEK®) for cancers or other diseases is significantly constrained due to high levels of variability in hepatic metabolism of the drug, dose dependent effects on the liver, and a negative food effect associated with the drug when administered with meals. The approved USPI notes that that riluzole tablets should be taken at least 1 hour before, or 2 hours after, a meal to avoid food-related decreases in bioavailability that may interfere with the ability to achieve or maintain therapeutic blood concentrations. Such fasting requirements amount to six hours of fasting per day when administered twice daily. Despite riluzole's approval over 20 years ago, these multiple clinical constraints of riluzole have persisted and limited the clinical application of riluzole to other disease states. We describe here prodrugs of riluzole in order to improve the clinical efficacy of riluzole-based therapy, increase patient compliance, and relieve human suffering. Metastatic melanoma has few treatment options, and the current therapeutic standard of care is dacarbazine which is a highly cytotoxic drug with severe side effects including vomiting, headache and hair loss. Treatment with dacarbazine has a median progression-free enhancement of survival time of only 1.5 months. Riluzole (Rilutek™) is a generally non-toxic drug and currently the only FDA-approved treatment for amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease).
We have recently shown that riluzole has dramatic anti-melanoma activity in vitro cellular assays, in mice and in a Phase 0 human clinical trial. In the clinic, four of twelve melanoma patients showed significant clinical or radiologic evidence of Stage III and IV tumor response. These results, along with the mild side-effect profile that riluzole has shown among ALS patients, suggests that this drug has significant potential for use as an improved treatment for metastatic melanoma. However, the therapeutic utility of riluzole itself in ALS and eventually for melanoma is very constrained by rapid first-pass metabolism in the liver and an exceptionally high level of patient-to-patient variability in the extent of the Cyp1A2-mediated oxidative metabolism that is observed.
Riluzole is also believed to be clinically relevant in additional disease states, including a variety of central nervous system (“CNS”) and depression/anxiety states. These include, but are not limited to, bipolar disorder, treatment resistant and major depression, obsessive-compulsive disorder, general anxiety disorder, panic disorder, social anxiety, mood disorders, cognitive disorders, dementia, agitation, apathy, psychoses, post-traumatic stress disorders, irritability, disinhibition, learning disorders, memory loss, personality disorders, bipolar disorders, Rett syndrome, eating disorders, conduct disorder, neurodegenerative disorders, pain disorders, supranuclear palsy, frontotemporal dementia, frontotemporal lobar degeneration, delirium, Alzheimer's disease, mild cognitive impairment, mild cognitive impairment due to Alzheimer's disease, drug addiction, tinnitus, mental retardation, spinal muscular atrophy, radiation therapy, multiple sclerosis, chronic cerebellar ataxia, hereditary spinocerebellar ataxia, spinocerebellar ataxia, sporadic ataxia, episodic ataxia, Friedreich Ataxia, Multisystem Atrophy, ataxia associated with Anti-GAD antibodies target and onconeural antigen, essential tremor, cervical spondylotic myelopathy, spinal cord injury, hereditary cerebellar ataxia, Tourette syndrome, autism spectrum disorder, schizophrenia, fragile X syndrome, Parkinson's Disease, Progressive Supranuclear Palsy, Dementia with Lewy Bodies, and Huntington's disease. However, riluzole can have issues in liver metabolism. Pro-drugs of riluzole will provide more predictable pharmacokinetic properties and metabolic profiles for the parent compound, leading to an improved therapeutic effect in each of the aforementioned disease states. Riluzole has been approved for 25 years without solutions to the pharmacokinetic and metabolic limitations of the drug. The intrinsic property of the drug itself teaches away from the sublingual administration of riluzole. Riluzole has a very low solubility in water, poor oral palatability, pH dependent chemical stability, and intense as well as persistent numbness or burning sensation throughout the oral cavity. Techniques aimed at reducing these undesirable effects, such as use of chelating agents, would only facilitate the oral swallowing and gastric absorption rather than resulting in sublingual absorption.
It has also been demonstrated that riluzole is clinically relevant to generalized anxiety disorder (GAD) and is useful for the attenuation of presynaptic glutamate release. Riluzole is also useful for the normalization, enhancement or potentiation of the uptake of glutamate by glia (Coric et al. U.S. Pat. No. 8,778,979).
There is a long felt need for new treatments for melanoma that are both disease-modifying and effective in treating patients that are refractory to current treatments. The present invention addresses the need to identify new treatments for melanoma by identifying novel prodrugs of riluzole which possess enhanced stability to hepatic metabolism and are delivered into systemic circulation by oral administration. The present invention can also treat or prevent various neurological or CNS states as well as depression/anxiety states. The riluzole prodrugs are cleaved to release riluzole in the plasma via either an enzymatic or general biophysical release process.